In recent years, with advance in digital technology, electronic devices such as mobile information devices and information consumer electronics have been developed to provide higher functionality. With the higher functionality of such electronic devices, there is a rapid progress in miniaturization and speeding up of semiconductor elements for use in the electronic devices. Among them, the usage of high-capacity nonvolatile memory device such as flash memory is rapidly expanding. Furthermore, as a next-generation nonvolatile memory device to replace the flash memory, research and development is under way for a nonvolatile memory device including a variable resistance nonvolatile memory element has a feature that a resistance value reversibly changes according to electrical signals.
FIG. 22 is a cross-sectional view showing a configuration of a conventional example of such nonvolatile memory element (for example, refer to Patent Literature 1 and Non Patent Literature 1). As shown in FIG. 22, in a nonvolatile memory device 1030, a transistor 1020 and a nonvolatile memory unit 101 are formed on a main surface of a semiconductor substrate 1024. The transistor 1020 is a circuit for controlling conduction to a bit line of the nonvolatile memory unit 1010, and comprises a source region 1025b, a drain region 1025a, a gate insulating film 1026, and a gate electrode 1027. The nonvolatile memory unit 1010 includes a bottom electrode 1002 connected to the drain region 1005a, a variable resistance layer 1003 in which a resistance reversibly changes according to a voltage pulse or a current pulse, and a top electrode 1004. Furthermore, the transistor 1020 and the nonvolatile memory unit 1010 formed above the semiconductor substrate 1024 are covered with an interlayer dielectric 1028, and the top electrode 1004 is connected to an electrode wiring 1029.
In Patent Literature 1, as a substance composed in the variable resistance layer 1003, one of nickel oxide (NiO), vanadium oxide (V2O5), zinc oxide (ZnO), niobium oxide (Nb2O5), titanium oxide (TiO2), tungsten oxide (WO3), cobalt oxide (CoO), and the like is used. It is known that such transition metal oxide shows a specific resistance value when a voltage or a current having greater than or equal to a threshold value is applied, and that the resistance value is maintained until a voltage or a current is newly applied. Moreover, in Non Patent Literature 1, as the substance composed in the variable resistance layer 1003, Pr(1-x)CaxMnO3 (PCMO) is used. A perovskite material is known to show the above described variable resistance property.